The overall goal of the research is to develop a computerized medical information system capable of accurately extracting medical knowledge pertaining to the therapy and evolution of chronic diseases from a database consisting of a collection of stored patient records. Computerized clinical databases have been of research interest throughout the world for at least a decade. Among the earliest of such endeavors was the ARAMIS Project (American Rheumatism Associaton Medical Information System) under development at Stanford since 1967. ARAMIS contains the records of thousands of patients with a variety of rheumatologic disorders. Similar databases exist for cancer, stroke, and heart disease. The fundamental goal of ARAMIS and other clinical database projects is to use the stored data to derive medical knowledge on the course, treatment, and consequences of treatment of the chronic diseases. Unfortunately, the process of reliably confirming hypotheses has proven to be refractory to purely statistical methods because of problems stemming from the complexity of disease, therapy, and outcome definitions, the complexity of time relationships, strong sources of bias, and problems of missing and outlying data. The objective of this project which we will call RX - emphasizing our interest in problems of therapy - is to explore the usefulness of knolwedge-based computational techniques in solving this problem of accurate knowledge inference from non-randomized, non-protocol patient records. The ARAMIS Database is used as a testbed for the project.